This invention relates to a rotary well pump system for pumping oil bearing material from a producing formation to the ground surface.
Rotary or screw pumps for oil bearing materials are well known which include a stator fixed to a outer tubing together with a rotor which is driven by a shaft leading from a suitable drive mechanism at the ground surface. The rotor and stator are cooperatively shaped to provide a pumping pressure which transmits the oil bearing materials from the pump through the tubing to the ground surface.
Examples of pumps of this type are sometimes known as Moineau pumps or progressing cavity pumps and are shown in U.S. Pat. Nos. 2,085,115 (Moineau), 2,267,459 (Hait), 2,456,227 (Wade), 2,749,992 (Hill), 3,347,169 (Cronin) and 4,580,955 (Karge).
Pumps of this type have been developed for pumping heavy oils which often contain sand materials. The design of the rotor and stator is particularly developed to handle the transmission of the sand provided the amount of sand remains below an acceptable maximum proportion of the liquid material.
However many pumps of this type have problems associated with sand and the levels of sand which are necessary for pumping to the surface. Sand production problems are generally regarded as the major cause of service expense in the production of heavy oil. Sand production is due in part to the velocity changes of fluids and gases entering the well bore. A well that occasionally experiences "gas kicks" often also has corresponding sand influxes. The conventional downhole pumping equipment is tolerant to relatively large amounts of sand provided the sand comes to the pump in a steady homogenous slurry with the remaining oil materials. However the sudden influx of sand into the well bore can often overwhelm the pump leading to a complete loss of production or reduction in the amount produced to an uneconomic level.
Various servicing procedures are available for overcoming this problem but these are of course in many cases lengthy, time consuming and expensive thus significantly interfering with the economics of the heavy oil production system.